Various components of conventional drill pipe, coiled tubing or other downhole tools may get stuck in the well bore at times. A jar may be used to deliver jarring blows to a tubing string in order to free a stuck component. Examples of jars include U.S. Pat. Nos. 5,906,239, 5,411,107, 5,495,902, and US patent publication no. 2009-0301707. Many such jars incorporate one or more internal valves that fit closely with a restriction or bowl on the inside of an internal chamber to create a pressure-differential and energy buildup for release in a jarring action.